Windows 7 Network Awareness: How Windows knows it has an internet connection

I thought this was a good article.

Have you ever been connecting to a new wireless network and seen the following pop-up balloon?

"Additional login information may be required. Click to open your browser."

Whenever I connect to a WiFi network which requires in-browser authentication, such as university networks and hotel access points, Windows somehow magically knows. Windows also knows when your internet connection isn’t working, and can differentiate between having local LAN access, no network access at all, or full internet access. But how?

This week’s question of the week is one I myself asked about this very topic. I guessed that there must be some online Microsoft site that Windows is checking to determine the state of the connection, but I wanted proof, not just speculation.